BACKGROUND: Greater early left ventricular mass index (LVMi) regression is associated with fewer hospitalizations 1 year after transcatheter aortic valve replacement (TAVR). The association between LVMi regression and longer-term post-TAVR outcomes is unclear. OBJECTIVES: The purpose of this study was to determine the association between LVMi regression at 1-year post-TAVR and clinical outcomes between 1 and 5 years. METHODS: Among intermediate- and high-risk patients who received TAVR in the PARTNER (Placement of Aortic Transcatheter Valves) I, II, and S3 trials or registries and were alive at 1 year, we included patients with baseline moderate or severe left ventricular hypertrophy (LVH) and paired measurements of LVMi at baseline and 1 year. The associations between LVMi regression (percent change between baseline and 1 year) and death or rehospitalization from 1 to 5 years were examined. RESULTS: Among 1,434 patients, LVMi was 146 g/m2 (interquartile range [IQR]: 133 to 168 g/m2) at baseline and decreased 14.5% (IQR: 4.2% to 26.1%) to 126 g/m2 (IQR: 106 to 148 g/m2) at 1 year. After adjustment, greater LVMi regression at 1 year was associated with lower all-cause death (adjusted hazard ratio [aHR]: 0.95 per 10% decrease in LVMi; 95% confidence interval [CI]: 0.91 to 0.98; p = 0.004; aHR of the quartile with greatest vs. least LVMi regression: 0.61; 95% CI: 0.43 to 0.86; p = 0.005). Severe LVH at 1 year was observed in 39%, which was independently associated with increased all-cause death (aHR of severe LVH vs. no LVH: 1.71; 95% CI: 1.20 to 2.44; p = 0.003). Similar associations were found for rates of cardiovascular mortality and rehospitalization. CONCLUSIONS: Among patients with moderate or severe LVH treated with TAVR who are alive at 1 year, greater LVMi regression at 1 year is associated with lower death and hospitalization rates to 5 years. These findings may have implications for the timing of valve replacement and the role of adjunctive medical therapy after TAVR.